The one problem with Xen is transparent high availability of your servers, sure you can snapshot an image but thats only of you shutdown the virtual machine. How excited was I when Remus announced that it has been applied to the official Xen repository, and is expected to be included with the next major release. Bookmark this page for a soon to be released how to install Xen with Remus support on CentOS 5.4!

What is Remus?

Remus provides transparent, comprehensive high availability to ordinary virtual machines running on the Xen virtual machine monitor. It does this by maintaining a completely up-to-date copy of a running VM on a backup server, which automatically activates if the primary server fails. Key features:

* The backup VM is an exact copy of the primary VM. When failure happens, it continues running on the backup host as if failure had never occurred.
* The backup is completely up-to-date. Even active TCP sessions are maintained without interruption.
* Protection is transparent. Existing guests can be protected without modifying them in any way.

For a full description and evaluation, see their NSDI paper.

Visit the project: http://dsg.cs.ubc.ca/remus/